The monitoring of industrial discharges in nature in liquid form is generally performed visually and by analysis of discharged liquid samples according to a specific method for each chemical species being investigated. Furthermore, when monitoring a large expanse of aqueous effluent that might comprise chemical species not uniformly distributed on said expanse, it is necessary to collect multiple samples at different sites in order to localize the origin of the production of said species. The time required for the analysis of the sample and the replacement rate of said effluent affect the diagnosis with regard to this localization.
Moreover, the detection of the appearance of a reaction compound by the collection of samples of the reaction medium present a double drawback. First of all, the reaction is affected by the collection of said sample and, second of all, the longer the time required for the analysis of said chemical compound in relation to the reaction rate and the lower the degree to which the monitoring of the reaction is possible.
In order to resolve this drawback, it has been envisaged to detect the presence of chemical species by spectroscopic means comprising means of electromagnetic excitation oriented to the medium to be analyzed and means for the spectroscopic analysis of the signal back-scattered by the surface of said medium. In this manner, the chemical species are identifiable essentially instantaneously without disturbing the medium.
However, the means of electromagnetic excitation directed on the medium to be analyzed excite a surface of the medium. Thus, on the one hand, the incident signal must be sufficiently strong so as to excite all of the species of the surface and, on the other hand, the means of detection must be extremely sensitive in order to detect the spectra of said chemical species of said surface.
It would therefore be advantageous to provide a method for the detection of chemical species present in a condensed medium which not only makes it possible to precisely detect the nature of the chemical species present in said condensed medium with less costly detection means, but also which enables excitation of the surface of said condensed medium with means of reduced power and thus equally less costly.